Pinpointing regulatory protein phosphatase 2A subunits involved in beneficial symbiosis between plants and microbes

Abstract

Background PROTEIN PHOSPHATASE 2A (PP2A) expression is crucial for the symbiotic association between plants and various microbes, and knowledge on these symbiotic processes is important for sustainable agriculture. Here we tested the hypothesis that PP2A regulatory subunits, especially B’φ and B’θ, are involved in signalling between plants and mycorrhizal fungi or plant-growth promoting bacteria. Results Treatment of tomato plants (Solanum lycopersicum) with the plant growth-promoting rhizobacteria (PGPR) Azospirillum brasilense and Pseudomonas simiae indicated a role for the PP2A B’θ subunit in responses to PGPR. Arbuscular mycorrhizal fungi influenced B’θ transcript levels in soil-grown plants with canonical arbuscular mycorrhizae. In plant roots, transcripts of B’φ were scarce under all conditions tested and at a lower level than all other PP2A subunit transcripts. In transformed tomato plants with 10-fold enhanced B’φ expression, mycorrhization frequency was decreased in vermiculite-grown plants. Furthermore, the high B’φ expression was related to abscisic acid and gibberellic acid responses known to be involved in plant growth and mycorrhization. B’φ overexpressor plants showed less vigorous growth, and although fruits were normal size, the number of seeds per fruit was reduced by 60% compared to the original cultivar. Conclusions Expression of the B’θ gene in tomato roots is strongly influenced by beneficial microbes. Analysis of B’φ overexpressor tomato plants and established tomato cultivars substantiated a function of B’φ in growth and development in addition to a role in mycorrhization.

“B” Regulatory Subunits of PP2A: Their Roles in Plant Development and Stress Reactions

“…An interesting study has revealed that low levels of B′φ transcripts are necessary for the proper formation of mycorrhizal associations in tomato roots to maintain normal plant development [ 55 ].…”

Distinct Clades of Protein Phosphatase 2A Regulatory B’/B56 Subunits Engage in Different Physiological Processes

“…A fifth clade, Φ, is also found in higher plants, but not in Arabidopsis, and appears to be involved in the interaction with mycorrhizal fungi. Arabidopsis and other Brassicaceae/Cleomaceae do not form mycorrhizal associations, and this could be the reason that B'φ has been lost from Arabidopsis [9,14,15]. The B' clades evolved after the division of eukaryotes into animals and plants, and there is no connection between the use of Greek letters for animal and plant B' subunits.…”